1. Field of the Invention
The present invention relates to a printing machine including an image forming unit adapted for formation of images on a recording medium in course of transfer on a transfer route, and a feeding method for printing machines.
2. Description of Related Arts
In the field of image forming devices including those of an inkjet system, there have been recent trends of diversification in, among other specifications, size and type of print sheets, accompanied by provision of a system of feed routes adapted for a sheet feed complying with any specification for print sheet to be used. Image forming devices generally have a mechanism configured with a set of rolls arranged in a transverse and/or normal opposing relation (referred herein to as a roller) installed for register on a transfer route, upstream of an image forming unit, to temporarily hold a print sheet as a recording medium fed from any feed mute, giving a slack, to thereby adjust a timing to send out the print sheet to set on the transfer route.
Each print sheet is transferred to the image forming unit, under a control consistent with an associated transfer condition that varies depending on the combination of a set of sheet specifications such as size and type of sheet and a set of route conditions such as curvature and distance of travel. If the register roller had a greater transfer speed than an upstream roller, there might have been a print sheet being retained by the upstream roller when pulled by the register roller, with a so-called back tension (by tensile forces acting) on the print sheet, which would have constituted a cause to generate noises upon removal of a slack produced by the register roller such as for adjustment of the timing to send out the print sheet, as an issue.
Such the back tension might also have constituted causes of a delay in transfer timing, a deviation of image position, and a jamming of sheet, involving an affect of the delay in transfer timing constituting an obstacle against image formation at higher processing rates, as another issue.
To avoid such issues, there has been a feed system disclosed in Japanese Patent Application Laid-open Publication No. 2002-167075 (referred herein to as a patent document 1), including a feeder configuration having a pair of feed rollers for gripping a print sheet to send out, and a drive mechanism for spacing feed rollers off from each other as necessary to release the print sheet from the gripping, for cancellation of back tensions.
There has been another feed system disclosed in Japanese Patent Application Laid-open Publication No. 2000-108482 (referred herein to as a patent document 2), including an assist roller installed upstream of a register roller on a transfer route, to assist the register roller transfer any specified type of print sheet at a transfer speed corresponding to the sheet type, to prevent the print sheet from failing to slack.